1. Field of the Invention
This invention relates to a printing press in which rainbow printing is done in a printing unit on a sheet supplied from a feeder.
2. Description of the Related Art
An inking device of a printing press, which supplies ink to the surface of a printing plate mounted on a plate cylinder, has an ink fountain for storing ink, and a group of rollers for uniformly distributing the ink, which flows out of the ink fountain, in different directions while transferring it. The ink transferred to an end portion of the group of rollers is supplied to the plate cylinder via an ink form roller.
The inking device for performing such an ink supply action (hereinafter referred to as an inker) rotates the rollers and levels the ink prior to inking the plate surface before printing is carried out. Among the above-mentioned group of rollers, an ink oscillating roller, which acts in a roller rotational axis direction (a lateral direction), is disposed for distributing ink during printing as well as ink conditioning. Driving for the ink oscillating roller has hitherto been linked to driving for the inker, and when the inker is actuated, an oscillating motion also occurs in an interlocked manner.
To prevent forgery or for other purposes, rainbow printing is performed for printing in inks of two or more colors placed on the same plate surface. To realize this rainbow printing, the inker feeds inks of two or more colors onto the same ink roller, and inks with a constant mixed color width are supplied to a sheet. The mixed color width is controlled by keeping an ink film constant based on a balance between the transfer of inks to the sheet and the supply of inks from the ink fountains, and oscillating the ink oscillating roller over a required width. Instability of the ink film results in the instability of the mixed color width.
In rainbow printing, if ink conditioning is performed, the thickness of the ink film on the roller increases, and the mixed color width changes, because no ink is transferred to the sheet. Thus, rainbow printing has generally been done without execution of ink conditioning. That is, the leveled state of ink has been stabilized, with printing started while the sheet is being passed. Some printing presses adopt a manual operation with the use of a mechanism for stopping an oscillating motion. In detail, the oscillation width is set to be 0 mm at the time of ink conditioning, and the oscillation width is returned again to the original value at the time of printing.
Hence, printing presses, which do not carry out ink conditioning, have posed the problem of an increase in the number of defective sheets. Printing presses, which perform a manual operation using a mechanism for stopping an oscillating motion, have presented the problem that the oscillation width has to be adjusted for each ink conditioning and for each printing, inducing an increase in the printing make-ready time.
Japanese Patent No. 2875856 discloses a technique with a dampener in which the oscillating motion of an oscillating rider interlocked with an oscillating roller via a lever and a spring is blocked during inspection, when no water is supplied, by restraining the lever by moving means comprising an air cylinder and a pin, thereby preventing the interlocking of the oscillating rider with the oscillating roller. This technique may be applied to the inker which does rainbow printing. In this case, however, when ink conditioning is switched to printing, it becomes necessary to actuate the moving means again, thereby releasing the restraint of the lever. Thus, the operation is tiresome. If the operator forgets to perform this operation, the problem arises that the oscillating motion of the ink oscillating roller does not take place, and rainbow printing cannot be achieved.